In the past, it was common practice to employ a three-position operative searchlight signal unit having an operating assembly which is located and mounted in a protective casing. The means for generating the luminous radiation includes a single lamp which emitted achromatic or white light. The light was focused at the conjugate focal point of a polished elliptical reflector and a plano convex objective lens. The optical filtering system included a three-position relay that positioned one of three colored roundel mobile assemblies interposed between the lamp and objective lens. When the relay is deenergized, it will assume a neutral control position to give a red indication. The other two positions have green and yellow color filters. Thus, these types of signal units must rely upon the transitional displacement by an electromechanical device which is a distinct disadvantage. In addition to the need of periodic maintenance, such as, lubricating and adjusting, there is always the possibility of mechanical breakdown or malfunction of the relay. In order to alleviate the shortcomings of such dynamic signal units, it was previously proposed to redesign the searchlight unit as a static device having no moving parts. The previous static searchlight signal unit employed a plurality of lamps and associated elliptical reflectors and color filters in combination with a pair of dichroic filters and objective lens to produce a colored signal light of one of a given number of colors. In practice, the dichroic filters are angularly-disposed at forty-five degrees (45.degree.) with respect to the axis of objective lens and to the axis of the focal point of some of the elliptical reflectors. Further, the dichroic filters are generally selected by their passband and rejection and angle of incidence is the determining factor for performance of the filtering action. In most cases, the dichroic filters are accurate over the visible spectrum within a range of plus or minus fifteen degrees (.+-.15.degree.) of the specified angle of incidence, and beyond this fifteen degree angle, the transmitted rays are shifted toward the red end of the spectrum. Presently, there are no dichroic reflectors available that can accommodate light rays that have a continually varying angle of incidence and, therefore, it is difficult and virtually impossible to conform the spectrum chromaticity required by the Association of American Railroads (AAR).